text:
Does the PA-44's squat switch disable the stall warning?
I've read the AFM and looked online about the gear system for the PA-44 Seminole and there is apparently a squat switch on the right main gear that disables the stall warning whilst on the ground. However during my pre-flight I have tested the stall warning with the battery master and avionics master on and it worked.
Is the stall warning squat switch not a feature on the newer PA-44s any more? The one I train in is about a year old now.

Are you sure you're talking about the stall warning? I believe you're talking about the horn that activates when in the landing configuration with no gear down(e.g throttle retarded, flaps down).
The 44 has 2 electric stall warning tabs that won't be actuated on the ground.

I think your answer is, "no, that aircraft never had a squat switch to disable the stall warning."  Which seems to be exactly the answer the OP needs. This post was flagged as "not an answer," which I think is incorrect, although a more direct phrasing of the response may help avoid such flags in the future.

I agree, think it's clear a no was implied in the answer, I'll try to be more direct in the future, thanks

A bit late on this but yes, the Seminole has a right main gear squat switch to disable the lift detectors on ground. The reason why you are able to test it, is because most operators or flight school disable it for this very reason. But yes, you’re right, it comes out of the factory with the lift detectors disabled by the right squat switch, not sure why.


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Do paper airplanes fly like normal airplanes do?
After a while of researching, I found that nobody actually knows how paper airplanes work and after experimenting myself, I can't really find much about it. If anybody does, have a good answer and has a better researching angle, please tell me.

Could you specify what you mean by actually? The aerodynamic forces on paper planes can be calculated with the same equations which predict the aerodynamics of a B747. Could you maybe point to a resource which states this lack of understanding?

Our current understanding / assumption of physics is that the laws of nature are the same in the entire universe. Since airplanes fly by the laws of nature, the only way that paper airplanes work differently than normal airplanes would be if they fly in a different universe with different laws of nature.

Navier-Stokes and basic physics apply to all.  Their Reynolds number is quite different of course, but that's just cause of their relative size. You may as well ask if the Spruce Goose (or WWI aircraft) fly differently because they're made of wood.

No that’s wrong. Paper airplanes fly by the same physics that allows a 747 to fly.

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text:
Does the radar altimeter's position affect its accuracy?
I have seen the location of the radar altimeter is different between Airbus and Boeing. Airbus has it almost at the tail, Boeing has it forwards. I would like to know which one gives the height more accurately?

Related, maybe a dupe?

Why would the mounting location affect accuracy? It should be calibrated for the installed location, so the accuracy should be relatively close between installations.

Possible duplicate of Where does the altimeter measure from?

As others have said, the radar altimeters must be calibrated. For the installation to be approved, they have to meet the specified accuracy requirements (ref: EUROCAE ED-30) regardless of where they are installed. That said, location can have an impact. Being too close to landing gear, other antennas, or other protuberances can be a problem.

I don't think the proposed duplicate adequately addresses this auestion, which has to do with accuracy in flight regimes and at varying deck angles, not merely location or calibration.

In the aircraft I fly, the radar altimeter (aka radio altimeter) is calibrated for the installation, and the calibration compensates for the flight attitude of the aircraft at touchdown.  The radar altimeter is considered radio navigation avionics, and in many cases is required equipment.
So in theory, a flight attitude other than a normal approach attitude may cause some error.  However, since the primary use is during approaches, the consequence of this error is negligible, assuming flaps and gear extended.
In practice the avionics tech verifies that the altimeter reads a certain reading on the ground, and that reading is within spec for the installation. Practically, this means that the radar altimeter does not always read "0" when the aircraft is on the ground in a taxi or parking mode, however it is normally close.
My assumption in answering this is civilian aircraft, using normal low level short range radio altimeters, as opposed to delay Doppler or synthetic aperture radar which are used for other types of navigation applications.

First, let's get the equipment straight - a RADAR altimeter uses a "pulse" transmission characteristic, and a RADIO altimeter is FM CW - both transmitters operate near or at 4.3GHZ.
The operating characteristics are different, the "pulse" system is fairly simple - you transmit a pulse, receive the pulse, and calculate the delay between the two for your altitude.
The FM CW transmits a Frequency Modulated Continuous Wave signal where the transmit signal varies in frequency from low to high within the 4.3GHZ center frequency (usually 400KHZ centered on 4.3GHZ) to give a 'sweep from 4.3GHZ minus 200KHZ to 4.3GHZ plus 200KHZ.  The FM CW receiver is phase locked to the transmit signal and compares the frequency shift (time delay of the FM CW sweep) of the receive signal to this signal, and derives a 'frequency change' which is translated to an altitude signal. The FM CW technique typically is less dependent on ground reflection anomalies and is more stable during approach.
The pulse type RADAR altimeter is widely used in military applications due to it's lower RF 'footprint' and is also used for terrain following autopilots.  Both systems respond to ground conditions, (moisture content) lakes, oceans - in different manners, and any object on the aircraft within a multiple wavelength of either system can result in a 'multi-path' signal reception and contribute to altitude error.  These errors from objects (other antennas, gear, flaps, even propeller blades at a particular RPM) may cause errors that are only observed during flight - this is the main reason for a flight performance evaluation.
The attitude of the aircraft during approach, say at the outer marker when flaps or speed settings are changed, will have slight variations, usually no more than +/- 10 feet, and as you approach closer to the ground this variation will become smaller - to the point of flare where the variation at 3 feet is less than 3 inches (with a 1.73 degree pitch angle approach).  At altitudes above a normal approach, the atmosphere (atmospheric rarefication, temperature, density, humidity and moisture content) can influence a radar pulse more than a continuous wave signal, and lightning can also have adverse affects on both radio and radar altimeters.

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text:
When are the engine bleed air, APU and packs turned on in the B737?
When do I have to turn on the engine bleed air and APU? In videos I have seen that they are always on, and sometimes they turn them off after take-off. I also have the same question about the packs.

Related, related (although not specific to the 737)

The general answer is, the engine bleeds stay on almost all the time.
The times they're turned off:

For a bleeds-off takeoff to get more power from the engines.
During deicing on the ground, so that deicing fluid doesn't get in the bleed air system.
When you are using the APU bleed air, the #1 engine bleed switch needs to be off IF that engine is running above idle power. If you're using APU bleed air & the isolation valve is open, the #2 engine bleed switch also needs to be off (if that engine is running above idle power).

The reason for the last requirement is because the engines, running above idle, put out greater bleed air pressure than the APU does, and you want to avoid the situation where the failure of a check-valve could put high pressure bleed air into the APU -- back-pressuring the APU, which could cause serious damage.
That scenario plays out if you're using the APU to run the cabin air conditioning (typically, on a hot day with lots of passengers), since it puts out a greater volume of bleed air than the engines do when they're operating at or near idle (i.e. typical taxi power settings). In that case, you close the engine bleeds, open the APU bleed and the isolation valve, and let the APU run both packs.
That scenario also plays out when starting an engine while taxiing; the switchology is reasonably intuitive but a little lengthy to describe.
There is no need when starting the engines initially to close the engine bleeds, since the normal procedure is to close the APU bleed & turn it off before taxiing the aircraft.
For a bleeds-off takeoff, the configuration is, engine bleeds off, APU bleed on, packs on, isolation valve closed. After takeoff, the steps are, #2 bleed on, pause, APU bleed off, pause, #1 bleed on, then isolation valve to Auto.
There is a procedure for a bleeds-off landing (to get more engine power for a go-around), and there are some QRH instances when you might turn a bleed switch off, but all of that is fairly rare.
If the OP is using a flight sim, the simple general answer, always leave the engine bleed switches on, will work fine.  Turn off the APU bleed after start. If you get the Master Caution for "Dual Bleed", you forgot to turn off the APU bleed, do so.
Edit, pack switches: off for engine start, on otherwise (except as directed by the QRH).

Is it possible to start engine 1 with both bleed air from the APU and engine 2 switched on?

@user19440  With the switches on, yes.  You wouldn't use bleed air from the #1 along with bleed air from the APU to do it, though. If #2 were running at idle, its bleed air output wouldn't be all that much compared to the APU. If the #2 were above idle, then you shouldn't have the APU bleed open. But it's entirely normal to start both motors with all 3 bleed switches in the on position.

"switchology" - I like that, I think I'll borrow it.  :)

APU Bleed air is usually turned on while starting the engine to supply them with enough pressure. After the engines have started, Engine Bleed is turned on an APU Bleed air is turned off as it's not needed anymore and the APU is being shut down.
For takeoff you can decide whether you keep the Engine Bleeds on or not. Having them turned off during the takeoff makes the engines more powerful.
After takeoff the engine bleed is turned on again to make sure the packs can supply fresh air to the cabin.

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text:
What are the best traffic pattern airspeeds in a Cessna 172N?
I have problems with my landings, and I would like to know what is the best speed
in the traffic pattern, especially on base and final? I am landing with 20 degrees flaps (in different weather conditions), and to be honest as a student pilot I am confused by the Cessna 172N POH, can anyone help?

Out of curiosity, what has your instructor said?

Have you read the POH? The recommended speeds are in there. What are you confused about in it?

Baseleg = 70 kts, Final  = 65 kts.

Section 4 of POH - Normal Procedures:

Section 4-3  of 172N POH - Normal procedures,  Speeds for normal Operation, Landing Approach: Normal Approach flaps up  60-70 KIAS, Normal Approach, flaps 40 degrees 55-65 KIAS, Short Field Approach, Flaps 40 degrees 60 KIAS, Balked Landing Maximum Power, Flaps 20 degrees 55 KIAS.  What is Normal Approach?  Base, Final ? In which weather conditions these speeds are valid? , For example: No winds, 40 degrees Celsius,  No winds  0 degrees Celsius?  Can  you understand confusion of student pilot when he/she hear question "Have you read POH" ?

The POH doesn't mention wind or temperature so you should assume no wind and disregard temperature. Wind really doesn't matter though as the speed is air speed. The only time you want to account for wind speed is if there are gusts, then you add half the gust speed to your air speed. Normal approach is just that, normal. The other types of approach are short field or soft field.

I'll echo @Notts90's comment above; have you discussed this with your instructor? What did he/she say? If you are finding the POH confusing, then it might not be a bad idea to schedule a session where you just sit down with your instructor and the two of you go through the POH without touching any of the knobs and switches in the actual airplane. You'll be expected to be familiar with the POH no later than by the time of your checkride, so might as well work on figuring it out now.

You guys must fly different planes than I do because none of the Owner's Handbooks that I have say anything about speeds and flaps in different parts of the traffic pattern. The general rule that we follow is to cross the threshold at 1.3 Vso and full flaps and manage your speeds, gear, and flaps in the pattern to reach that number. Short field is a bit slower.

Assuming 30 degree flags, cross the fence at 60-65 knots, touchdown at 60

This is really something you should discuss with your instructor, but if you want some general guidance then this should work:

Downwind: 70kts, 10° flaps
Base: 65kt, 20° flaps
Final: 60kts, 30° flaps

I say "guidance" because you may need to adjust this but it is in line with the POH values that you quoted in your comment and FWIW it's what I would use 'by default' in an unfamiliar C172. Although personally I wouldn't use 40° of flaps unless it's a short-field landing: the aircraft will come down more quickly with them fully extended.
But I'm not an instructor and I don't want to make assumptions about what he's teaching you and why, so you should definitely ask him this question. Ask him what power setting (RPM) he recommends on each leg, too.


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Is a stall warning horn required to fly?
I need an answer in reference to 14 CFR 23.207. I looked there and couldn't say 100% if it was a yes or a no.

No, many aircraft don't have them, like the Cherokee since it uses a gear warning horn. The horn signifies that the gear isn't down and you don't want to confuse that with the stall warning, so they don't have one.
23.207 says that an audible or visual indication is not required as long as the aircraft exhibits a "warning" 5 knots before the stall, in the case of the Piper Comanche the warning that satisfies the requirement is the stall buffet.
The relevant section of 23.207 is part (b):

(b) The stall warning may be furnished either through the inherent aerodynamic qualities of the airplane or by a device that will give clearly distinguishable indications under expected conditions of flight. However, a visual stall warning device that requires the attention of the crew within the cockpit is not acceptable by itself.

So the stall buffet, as long as it is pronounced, is adequate indication of a stall to satisfy 23.207.

Excellent thank you so much !!

At least some Cherokees also have a red light on the instrument panel as a stall warning.

@Bianfable The one I flew did not. Either way the regulation says that a "visual stall warning device ... is not acceptable by itself".

Most, perhaps all, Cherokees have fixed gear.  (The PA-28R models are usually called the Arrow, I think.)  Mine (1965) does have the red light on the panel as the stall warning, but it's very easy to feel the onset of a stall without it.

@jamesqf You're right, I was thinking of the Comanche, not sure why I said Cherokee.

@RonBeyer Stall warning was an option on the Comanche. My CFI’s Comanche does not have a stall warning light or buzzer. Nor does it have a gear warning like some Arrows.

The answer above is just flat-out wrong. It makes no difference whether or not certain airplanes have them or not when it comes to airworthiness.
The real answer is it depends...
91.205 does not include a stall horning but that doesn’t mean the Type Certificate Data Sheet for the plane you are piloting contains something different.
For example, a Cessna 172’s TDC (3A12) explicitly states that a stall warning horn is REQUIRED for the plane to be, well, a Cessna 172. Therefore if you are about to take off in a 172, you technically need an operational stall horn to be airworthy.
Generally speaking, you need to consult 91.205, the TDC for the plane, any STCs (supplemental), and then the MEL from the POH and probably in that order.
I highly recommend listening to the Max Trescott’s Aviation News Podcast episode 151 on airworthiness where they go through how to determine if a piece of equipment is required or not (hint: they talk about the stall horn!).

I fail to see where the contradiction in your answer relative to the one of Ron is. Yes, a stall warning horn is required for the 172, but not for the Arrow. Since the question is about 23.207 (and not the 172), Ron's answer is correct.

I guess I’m confused - where does the original question specify a Piper anything? Ron’s question is correct for the plane he mentioned. But you MUST MUST look at the type data certificate sheet as part of your SOP when dealing with inoperative or missing equipment. I gave the 172 as just one example where applying the original logic would yield the wrong answer. The person asking this question may switch planes, apply Ron’s logic, and be 100% illegal. I kind of find it funny i got downvoted for the correct answer.

First, I did not downvote your answer. Second, Ron's answer is correct, apart from the Comanche - Cherokee mixup. Buffeting is considered sufficient if it satisfies 23.205. Yes, the plane requires a horn (and not a 'horning') when the type certificate says it needs one. But that is only a consequence of 23.205. Basically, Ron's answer  is the engineer's answer and yours the lawyer's answer. And guess which one is more helpful!

I didn’t say you did btw (downvote). I agree about buffeting but If it’s on the type data certificate sheet it’s required regardless how useful the horn actually is or isn’t or this plane doesn’t need it cause of this or that. I DO agree with the fact that Ron’s answer is useful as practical knowledge goes if ultimately not complete from a reg standpoint.

OK, last attempt. The stall horn has been added in order to certify the 172. Without it the 172 would not comply with 23.207 (not 205). As a consequence of that, it is listed in the MEL. Without the horn the 172 cannot not be operated legally. The question asks whether every airplane needs a stall horn, and buffeting on the Comanche is sufficient to not require one. Ron's answer addresses this point directly and your explanation only explains how to find out whether one is required when certification made one necessary, but not why it has been added in the first place.

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text:
How can I find examples of airports with specific approach types?
Can you guys help me find airports with these approaches:

An airport with only an LNAV mins (so no LNAV/VNAV or anything other than just LNAV)
One with an LPV lower than 200 feet
One with an ASR approach. And what is an ASR approach?

There are no LPVs with a DA lower than 200' AGL.  https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/approaches

All ASR and PAR approaches are listed in the current Terminal Procedures Packet.
They are not listed with the other approaches but in the front matter after the alternate airport section.  I have never seen a PAR approach not associated with a military airport.  There are joint use military/civilian airports that have PAR approaches and allow civilians to fly them.

An ASR approach is an Approach Surveillance Radar style approach. The guys on MZeroA.com flew one in this video at KLAN. They are not "at" any airport nor are there plates for them it is effectively a function of ATC. I have heard them flown at a few "smaller" class D facilities near me for practice. Generally to practice them you need to be somewhere that ATC does not mind clogging the radio up as they take a fair bit of radio work to fly.
The RNAV (GPS) RW1 into KWWD has only LNAV minimums. (Note: It also has circling minimums which most LNAV airports will have unless terrain or some other issue forbids a circling maneuver).
As far as I know there are no LPV approaches that take you lower than 200 feet as is regulated by the FAA:

Localizer Performance with Vertical Guidance (LPV). An RNAV function
  requiring WAAS, using a final approach segment (FAS) data block, which
  computes, displays and provides both horizontal and approved vertical
  approach navigation to minimums as low as 200 foot ceiling and ½ mile
  visibility.

Best bet for ASR approaches are current or former military fields, especially Navy fields. You can usually fly an approach to a USAF field if they're not super busy (not sure about Navy/USMC fields), and if you call ahead they'll tell you when they expect less busy times. They won't let you touch down usually, but you can fly the approach to a go-around

ASR approaches are in fact "at" airports, very much so, for two reasons: 1) the controllers need special training in order to do them and must maintain currency on the procedure, and 2) the approach path needs to be flight checked just as for any other approach. That is why specific minima are published for radar approaches to specific runways at specific airports.


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When I use a plotter to identify a direction from a VOR, what heading or course is it exactly?
When I use my ASA IFR plotter and I'm working off a VOR, what direction am I getting? True course, true heading, magnetic heading, magnetic course?

I trimmed down your question a little to focus on the specific VOR question. Your broader question of "how do I use a plotter?" is fairly broad and might not fit this site's Q&A style well. If you aren't able to follow the instructions then you can certainly ask about that, I'd just suggest focusing on one specific task or issue at a time. And it would be great to include the text of the instruction and what you've already tried or understood.

If you are using a sectional chart and a plotter only, with no other information, remember the following:

If you are using the plotter relative to the sectional grid lines, you are measuring True Course.
If you are using the plotter relative to the compass rose around the VOR, you are measuring Magnetic Course.
True and Magnetic Heading can not be measured directly using the sectional and plotter. It must be calculated. You need to have the wind speed and direction to calculate any heading direction. You can calculate True Heading from Magnetic Heading. You can calculate Magnetic Heading from True Heading.
If you are in the aircraft, you can measure your Magnetic Heading by looking at your Magnetic Compass. You can calculate your True Heading from the Magnetic Heading, using the Magnetic Deviation, and the Magnetic Variation. Conversely, you can calculate your Magnetic Heading from your True Heading using the Magnetic Deviation, and the Magnetic Variation.


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Can an IFR civilian aircraft use a TACAN for DME distances?
Flying the KRDR LOC RWY 35 approach. How do I get my DME distance to HONNE or CANLI? can we pick up DME distance from a TACAN? Just used GPS Overlay but can we get distance from the TACAN?

Does this answer your question? https://aviation.stackexchange.com/a/29846

Thanks for the reply. It does help somewhat. The issue I had was that I couldn't pick up any distance at all when I was flying it. Even though I tuned the TACAN frequency in.

@757toga: Or in ICAO Annex 10.


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What does the "Caution" box mean on the sectional near Half Moon Bay, California?
What does this Caution box on the sectional chart near Half Moon Bay, California mean? Is there an official reference for the meaning of this box?

This one is a bit confusing and interestingly there is nothing in the FAA's sectional guide on "Caution" boxes although they do appear on other charts as well.
This one in particular is a warning that you will need monitor the radio for the transition routes below 2000 ft. If you can zoom in or get TAC level map resolution you will see a different warning

(source)
If you note a bit south of half moon bay the chart makes note of the fact you should be using the TAC in that area:

(source)

I don't think the answer is correct. Below 4,000-6,000 you are outside class B and you don't need ATC - it is a VFR Flyway. The VFR Transition Route is above 4,000-6,000.

@rvernica I read that as the flyway being "Below 6000 or Below 4000" depending on where you are, not above.

@Dave that is correct, the flyway is below and ATC clearance is not required on the flyway.

@rvernica is it just a monitor the frequency situation? Ill update the answer to be a bit more vague


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What is the difference between a published and unpublished TFR?
On this article about Sporting Event TFRs on the Flight Service website, they mention unpublished TFRs:

Play Ball! Be Aware of Sporting Event TFRs June 26, 2016 when you ask
the specialist for TFRs along your route of flight or request an
online briefing, you may expect the specialist to provide unpublished
TFR information that is not associated with the “blanket” sporting
event TFR. Ensure you check your route of flight for the possibility
of a Sporting Event TFR or published TFR.

What is the difference between a published and unpublished TFR?
From the article I would infer that Sporting Event TFRs are considered published, but I don't think they are published anywhere else but in the NOTAM. Appearing in a NOTAM is not considered as being published, right?
Where are the published TFRs being published now? NOTAMs used to be published in Notice to Airman Publication (NTAP). But, from these notes on the FAA website it seems that NTAP is being retired. So, where would the NOTAMS be published moving forward?

Can you quote the wording from the article? The link you posted just takes me to the homepage.

Play Ball! Be Aware of Sporting Event TFRs June 26, 2016 when you ask the specialist for TFRs along your route of flight or request an online briefing, you may expect the specialist to provide unpublished TFR information that is not associated with the “blanket” sporting event TFR. Ensure you check your route of flight for the possibility of a Sporting Event TFR or published TFR.

It looks like you have two questions: what's an unpublished TFR, and where are NOTAMS published?
First, unpublished TFRs. I can't find any FAA information on "unpublished TFRs" and I suspect it was just poor phrasing from FSS. I read the article you linked and it's unclear what they really meant, at least to me. Having said that, you could interpret "unpublished TFR information" in two ways:

Unpublished information about TFRs
Information about unpublished TFRs

I believe the intention was #1. There's a blanket 'stadium TFR' NOTAM but it doesn't include key information, like when the TFR is active for a given stadium. That's because games schedules change and the FAA doesn't keep track of them; it's up to the pilot to know if there's a game going on or not. For that reason, the stadium TFRs are very unpopular with pilots.
But, FSS might still tell you if a stadium TFR is active. Especially for major, high-profile events like the Super Bowl. There's no guarantee that they can or will, though, especially since FSS has become more centralized and less local.
Second, NOTAMs. The FAA currently publishes them here: https://notams.aim.faa.gov/#News
I say "currently" because the FAA seems to like moving things around and breaking links. But as you can see from that site, you can search yourself and there's also an interface that other systems can use.
Finally, that brings me to the practical answer to both your questions: just use your favorite flight planning app. I use Garmin Pilot, which displays current and future TFRs, and it keeps track of sporting event schedules. It also has NOTAMs, of course. Foreflight or other alternatives would do that too, I'm sure.
The stadium TFRs are usually easy enough to work around because - except for really big events like the Super Bowl - you can fly through them anyway if you're talking to ATC. So if you can get flight following (always a good idea) then you're complying with the TFR requirements.

I was on flight following and unaware of a stadium TFR. ATC informed me and asked me to go around the entire surface-area class C next to the stadium.

You can also find TFRs at https://tfr.faa.gov/ without having to sort through the NOTAMs.


text:
DC Generator on hotel mode ATR 72-600

Does the time an ATR 72-600 is running in hotel mode contribute to the flight hour (FH) limit of the DC Generator?
Does running an ATR 72-600 in hotel mode degrade the DC Generator brush differently than running the engine in normal operation?

It's not a good question if I have to look up every term in it to find out what the question means. Even having done so, I still don't know what you're asking. (Oh, I did know what an ATR72 is)

Added link to ASE post about hotel mode.

I'm nominating to re-open this question after the edits by LStrom. @AndiSetiawan If this is not what you wanted to know, please edit to clarify!

@JohnK, thanks for making it clear.

To start, the FH timer starts when the aircraft takes off (weight-off-wheels) and stops when the aircraft lands (weight-on-wheels).  This means that whether the engine is in hotel mode or running for taxi, the aircraft (and the DC Gen) are not accumulating FHs.  One thing to consider is the difference between an engine hour (EH) and a flight hour.  Engines have hard time limits based on how many hours the engine was run, not on how many hours it is in flight.  One might think that since the DC Gen is directly driven by the engine, that the wear rate should be based on EH, and I might agree with them. However, since the DC Gen is an accessory component (isn't a PWC part, doesn't come with the PW127 engine), the component is lumped in with the rest of the airframe systems, FHs are accumulated just like any other system outside the engine.
You would be right in saying that some aircraft components have hard time limits, that at a certain number of FHs, they need to be replaced. Good examples would be the engine (for overhaul), landing gear and some structure.  The components and the aircraft as a whole lose its certification if the hard time limits are exceeded.  The DC Gen however, more than likely has a soft time limit.  This means that the DC Gen is certified to be on the aircraft until it malfunctions.  The manufacturer of the DC Gen would likely impose a soft time limit, meaning that if the soft time limit is exceeded, it is out of warranty.
When the engine is in hotel mode, the only difference is that the prop and the turbine powering the prop are arrested.  The LP and HP sections of the engine are running as they normally would during taxi.  This post has some helpful images on what the internals of a turboprop look like (reference the second image, the first one is a PT6 I believe).  Hot exhaust air is still rushing past the arrested turbine that would normally power the prop.  This may cause some back pressure that the Full Authority Digital Engine Controller (FADEC) would need to account for, but in terms of the speeds and torque seen by the HP section, accessory drive and DC Gen, the wear seen on the brushes of the DC Gen would be no more than the wear seen during an engine taxi.

While your definition of flight hours is correct, they are very often used as a synonym for engine hours (or Hobbs time in GA), even in design documents. Also, welcome to the site! I hope you stick around.

What I've found is that you're right, FHs, EHs and Hobbs are synonymous when operating a commercial aircraft.  In terms of maintenance of an aircraft, agreements between manufacturers are very clear whether their warranty or required O/H is based on FH, EH or even flight cycles (FC).  Maintenance planners need to plan based on the components defined life limit, so FH and EH are tracked separately.   Thanks for the welcome!  I've been lurking for a while, finally found a question I could contribute to


text:
Is this legal to fly with passengers at dusk or dawn without night currency?
In USA, as per 14 CFR § 61.57, night currency requires three full stop takeoff/landings one hour after sunset and one hour before sunrise.
If a pilot is NOT night current but is day current, does the rules implicitly mean within the hour after sunset and within the hour before sunrise, is also considered part of the day currency?
As an example, the PIC can fly with passengers during this time frame even though it may be dark?

Yes.
Per 14 CFR 61.57:

Except as provided in paragraph (e) of this section, no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and—

It's worded as a negative, but if you are day current you can act as PIC with passengers during the times specified.
It's worth noting that there are different regulations that cover logging night time, or when lights are required.  Here is a link to an article explaining these differences:  When can you log night flight and night landings?

The 1 hour before/ 1 hour after rule is for logging currency only. The "night" time for carrying passengers is the end of evening civil twilight to beginning of morning civil twilight which is defined as the sun being 6 degrees below the horizon. This time completely depends on your latitude and time of year. In the lower 49 states (minus Alaska) the average time for civil twilight is approximately 20-30 minutes after sunset/20-30 minutes before sunrise. So if you are flying in the evening, you have about 20-30 minutes after sunset where it is legal without night currency, but after that, it is illegal.

34-37 minutes at 45deg latitude (portland), 30-33 minutes at 40deg (nyc), 28-29 minutes at 35deg latitude (los angeles), 27 minutes at 30deg (orlando). 20-30 is a good rule of thumb, just giving winter (short) and summer (long) times.

No, 61.57 says you can act as PIC with pax 1 hour past sunset.  Logging is different, you just got your regs mixed up... (see the link in my answer)


text:
What is the meaning of sub-paragraph 3-9-6 j. in FAA JO 7110.65X?
In JO 7110.65X, section 3-9-6(j) says in reference to the 3 minute rule:

j. Separate an aircraft behind another aircraft that has departed or
  made a low/missed approach when utilizing opposite direction takeoffs
  or landings on the same or parallel runways separated by less than
  2,500 feet by the following minima:

Heavy, large, or small behind super − 4 minutes.
Heavy, large, or small behind heavy − 3 minutes

Do you think this applies to an aircraft in the pattern making approaches to the runway in use after a heavy departs opposite direction?

If you search for the words "opposite direction" in the order it seems clear that they simply mean what they say, e.g. 3-9-7(a)(1):

Separate a small aircraft weighing 12,500 lbs. or less taking off from
  an intersection on the same runway (same or opposite direction
  takeoff) [...]

This is confirmed in JO7210.3AA, Facility Operation and Administration:

2−1−31. OPPOSITE DIRECTION OPERATIONS
Opposite Direction Operations consists of IFR/VFR Operations conducted
  to the same or parallel runway where an aircraft is operating in a
  reciprocal direction of another aircraft arriving, departing, or
  conducting an approach.


text:
How are batteries cooled in passenger aircraft?
What sort of systems are used to cool batteries in the air? Liquid cooled? Air cooled?
I am interested in lithium chemistry batteries in the form of either pouch cells or 18650 batteries inside of boxes placed in the fuselage or wing.

What type of batteries are you interested in?

Lithium chemistry batteries such as Li-Ion or Li-Po

As far as I can tell, current aviation lithium batteries do not use active cooling.
I know the True Blue Power TB17 (Robinson R44 & R66, Bell 505 Jet Ranger X) and TB44 (Cessna Caravan, DHC-6, DHC-8) do not require active cooling.
I haven't seen any easily accessible info on the Saft batteries for the A350.

From this presentation for the A320 family:

Battery ventilation
Achieved by ambient air being drawn around the batteries and then vented directly outboard via a venturi.

So the ventilation air provides cooling as well, especially when at cruise altitude. Batteries in the avionics bay are further cooled by a separate aircon system. From the same presentation:

Does the A320 family uses Li batteries?

@mins From what I've found, the A320 family uses NiCd batteries.

@selectstriker2: I got that info too, so the post doesn't answer the question which is about "lithium chemistry batteries".

@mins I can remove it if required.

"Ventilation" makes it sound like the primary purpose is preventing buildup of corrosive and/or flammable gaseous chemicals, not cooling?

@rackandboneman Could be. The fan blow in cold air though.


text:
Where can I find the regulations on the minimum stall speed for a GA aircraft?
I am designing a new GA aircraft that will enter service in 2028. I am looking for the FARS specifying the required minimum stall speed but different sources seem to say different things. On Cornell's Law school website, the Vstall is specified in 23.49. I found the same info on another site.
However, when I check eCFR, 23.49 doesn't exist. In fact, the regulations seem to end at 23.262. Were these other regulations amended or deleted? Which source should I use?

Part 23 has been completely rewritten; see this meta question for some related information

On August 30, 2017, a completely new body of regulations for small aircraft has been put in place which does not distinguish between normal or utility airplanes but low speed (below 250 KTAS) and high speed designs (> 250 KTAS). It also distinguishes between four levels depending on the number of seats (0-1, 2-6, 7-9 and 10-19 passengers). The spirit of the new regulation is to no longer prescribe design-specific rules but more abstract goals in order to limit risk, leaving the details to the aircraft builder.
Also, the number of rules has been drastically cut, and their numbering starts where the old numbering ended. Therefore, 23.49 has become 23.2110 and no longer gives a specific stall speed. All it does is to direct the applicant to determine a stall speed and details what conditions must be covered.
I expect that you have not formally started the certification process of your design, because that date determines which regulations apply. You are now free to select the stall speed of your design as long as you can demonstrate that the aircraft can be operated safely without exceptional pilot skill or strength.
But you can always count on Eurocrats when a body of regulations which has grown like cancer is to be preserved and extended. In their version (CS-23), the maximum stall speed of 113 km/h or 61 knots is still alive and well. However, Amendment 5 has now copied the new body of regulations as well and replaces the old certification standard in the name of global harmonization.
The old regulations reflect the experience which has been collected over decades. Many rules can be traced back to a specific accident and it helps to read through them and to consider why this specific rule has been implemented. Your new design might employ a clever way to avoid that particular condition at all, and then the new liberty of the new regulations will be helpful. But it would be foolish to throw all that experience overboard - a lower stall speed makes any airplane easier to fly. When things happen less quickly and less kinetic energy is involved, more accidents can be avoided and the damage in those that still occur will be lower.

Vs is dependent on the aircraft and is indicated on the air speed indicator of the aircraft you are flying. You will also find it in the flight envelope diagram.
FARs on the other hand are US regulations. They are organized into parts which do have versions, as you have already guessed.
Part 23 defines airworthiness standards to get an airplane type certified.
For single engine types, the stall speed is specified as less than 61 knots.
To complicate matters, even current aircraft may be certified to an older standard.
So if you want to know the Vs you have to tell us the plane type.

Thanks for the response! The craft is a general aviation aircraft with an EIS of 2028. The Vs part is primarily just an example. I'm just confused on what regulations I should use to restrict the design.


text:
What is the history behind CAR 105.01(2)?
Canadian Aviation Regulation 105.01(2) states:
"No person shall conduct an aerial sightseeing flight, or any portion of an aerial sightseeing flight, in the control zone of the Québec/Jean Lesage International Airport unless the flight commences at that airport."
I find it odd that this is a law, and not just a NOTAM.
Does anyone know why this was added to the CARs in 1998?

In short, it's because of complaints about noise. From the Canada Gazette, Vol. 132, No. 2, pp.98-103:

The regulation reflects the Minister’s desire to have increased
  oversight of sightseeing flights within the Québec/Jean-Lesage
  International Airport control zone.
[...]
The regulations are
  intended to prevent frequent low level flights for aerial sightseeing
  purposes over the built-up area within the Québec/Jean-Lesage
  International Airport control zone and to stop commercial
  passenger-carrying aerial sightseeing flights from using the Lac
  St-Augustin, Quebec aerodrome for either take-offs or landings. The
  prohibition of low level commercial aerial sightseeing flights within
  the entire Québec/JeanLesage International Airport control zone is
  intended to ensure that such operations do not relocate to another
  nearby lake and recommence sightseeing operations from that location.
[...]
Since the late sixties and, increasingly, in recent years,
  Transport Canada has received numerous complaints from citizens about
  the noise of floatplanes flying over several towns and cities in the
  Quebec City area.

The Gazette goes into a lot more detail about the background, impact, consultation process etc. 25 local mayors signed a letter to Transport Canada asking for action, so I guess it came down to political pressure in the end.


text:
What happens when flying on a Victor airway but through a class B or C airspace?
I think it´s a very simple doubt but also very important, and i can´t find the answer. If you are flying on a Federal Airway that at some point cross a class B airspace (for example)...do you need authorization or can you keep flying without one?

Welcome to aviation.SE! Are you asking about VFR or IFR?

Ask for Flight Following on your flights, they will more than likely help you out in those situations.

If you are flying your IFR flight plan which you got clearance for, then you have permission already.
If you are flying VFR you need to ask ATC for clearance.
Class B airspace requires clearance for all traffic and separation is also provided by ATC for all traffic.


text:
What's the relationship between AOA and airspeed?
We know that any aircraft will stall at its stall speed (for a specific weight, CG position, etc.) but also, that the same airplane will always stall at the same angle of attack.
I´ve read that IAS is just the easy way to control AOA, because in reality it's all about AOA and nothing to do with airspeed. That when changing IAS we are changing the relative wind and thence AOA. On the other hand, I know that the critical AOA doesn´t change with weight (it will always be the same for a given airfoil) but the stall speed will.
There are also high speed stalls... I'm confused. Can we get into a stall without reaching the critical AOA? What's exactly the relationship between AOA and IAS?

The angle of attack for the stall is always the same, as you already understood correctly. Depending on the load that you put on the wing, either by pulling more g's in a dive (high speed stall) or in a steep turn or by increasing the weight of the aircraft, you change the necessary speed to create enough lift. Think of it like this: Stall speed is your IAS as your angle of attack reaches the critical angle of attack. That means stall speed can be literally anything from 0 to vmax if you pull between 0gs or pull over g's or put too much load in the aircraft.

"Can we get into a stall without reaching the critical AOA?" -- no.
"We know that any aircraft will stall at its stall speed (for a specific weight, CG position, etc.)"-- we need to add "G-loading" to this list of parameters.  The "stall speed" we usually talk about is the 1-G stall speed.  Change the weight or the G-loading, and the airspeed correlating to the stall angle-of-attack changes.
"On the other hand, I know that the critical AOA doesn't change with weight"-- correct, but for a given G-loading, such as 1 G, the airspeed correlating to that critical AOA scales according to the square root of the weight.
"What's exactly the relationship between AOA and IAS?" -- if we know the IAS where the wing reaches the stall AOA at some given weight and G-loading, then we can adjust that IAS for some other condition by multiplying by the square root of the change in weight times the square root of the change in G-loading.  "Change in" meaning the ratio, i.e. new divided by initial.
The fundamental relationship between AOA and IAS is that net lift force at any given AOA is proportional to airspeed (IAS) squared.
Here's an extra complication that you may not want to worry about right now -- the "dynamic stall" -- What is the immediate cause of stall? -- scroll down to last paragraph.

A practical answer to help you understand critical angle of attack and stall speeds would be the operation of fast jets. The quickest way to land a jet is to join for a ‘run-in and break’ this could be at any speed but typically 350kts. A high-g turn would be used from overhead the runway at circuit height to the downwind position. The aircraft would be pulled into the turn until the stall buffet was achieved. This stall and associated drag slows the aircraft quickly and easily to the approach speed. Because the aircraft is above the minimum stall and retains lots of energy a reduction of control forces at any point would reestablish normal flight. Although the aircraft would experience a ‘stall’ at high speed due to the critical AOA being exceeded, the same aircraft would stall at about 100kts straight and level.

Close, but there are a few errors in this:  First, the break turn is typically performed 500’ above pattern altitude.  Second, the aircraft does not “experience a stall at high speed due to critical AOA being exceeded”.  That would be very bad.  Typically the target in the break is max lift AOA to use all the induced drag available to slow down.  Even pre-stall buffet is too much pull.  Good point though that accelerated stall recovery is easy because you have lots of energy.  With airspeed above straight and level stall speed, simply relax the pull and you are safe again.

The direct answer to the question as it is ("What´s the relationship between AOA and Airspeed?") is simple: none whatsoever -- that is, until you introduce context and some conditions.
Your context is: we want an airplane to fly. And not just 'fly' but to keep level, at least. For that, you need a certain amount of lift. Lift is used to counteract weight, so you need at least that much to fly level. Plus, you'll need some extra to pull most manoeuvres (such as turns).
The way airplanes create lift is by using wings. If we 'fix' the wing for simplicity (that is, forget about flaps and other devices that change the wing1), there will be only two variables under the pilot's control that effect lift:

Angle of attack (AoA).
Airspeed. (Pilots usually talk about indicated (or calibrated) airspeed rather than true airspeed. It implicitly includes air density and thus altitude).

The more of each, the more lift. The dependency is quadratic on airspeed (double airspeed, 4x the lift), and more or less linear on AoA (until you get closer to stall).
What determines stall is, in practice, solely the AoA,2 as you already understand. If you had an accurate AoA sensor, that's all you'd need to watch in order to avoid stall. (But you'd still need to have knowledge of how the airplane flies, i.e. the above dependencies, in order to know what to do to avoid it).
However, for various reasons you usually don't have such sensor. In this case you can use airspeed as a proxy. But airspeed is linked to AoA via lift, as we discussed. You need to know the current lift, too! How do you know it? Well, in a straight and level flight, lift exactly equals weight, by definition. You know your weight because you filled in the weight & balance chart prior to flight, right? You also know how much fuel you used up to this point.
So, the heavier your given airplane is (say, if you load an extra passenger), the more lift you'll need in the same conditions. And as we know, we can create this extra lift in two ways: by increasing AoA or by increasing airspeed, or both. If we just increase AoA, we'll obviously get closer to stall, and at some point we'll stall - at the same airspeed as we were perfectly able to fly with lower weight. Or, the other way round, if we 'fix' AoA (say, consider the stall AoA - which is fixed, as we know), we'll need higher airspeed for higher weight. (1.4x airspeed for double weight).
This is why your stall speed varies with weight. It also varies with G-loading, which is the case when the wing needs to create more lift than weight. (Coordinated turn is the first manoeuvre that pilots learn when this happens). When the documents (such as POH) specify 'stall speed', they also specify the weight at which it applies. (If they don't, they conservatively imply maximum permitted weight). They also often have charts how the stall airspeed increases in turns (as a function of the bank angle).
So, when we talk about 'stall airspeed', we understand it as 'airspeed at which the wing produces the required amount of lift while being at the stall AoA'. The 'required amount', in turn, depends on the conditions being considered: for the simplest case of straight and level flight, this is just the weight.

1 As well as about ice, bugs and dirt on the surface, etc.
2 In truth, true airspeed also has an effect via Reynolds number (Re), but in the context of GA this effect is very minor. The rate of change of AoA also matters, but only for very aggressive manoeuvres, like in aerobatics.

The relationship between AOA and airspeed is beautifully explained in the Lift Equation:
$Lift$ = Air density x Wing Area x Lift Coefficient (Camber and AOA) x V$^2$.

IAS is an easy way to control AOA

Theoretically, yes.  In reality, not very practical because airspeed cannot be instantaneously changed by adding thrust.  This is especially true when the aircraft is bigger, like an airliner.
Inertia (mass) must be overcome to move at all, as shown by the Acceleration Equation:
$Force$ = Mass x Acceleration
Rearranging to: Acceleration = Force/Mass
It is airspeed that creates lift, so we must keep adding thrust until we are going fast enough to fly (as on the run way taking off).

can we get into a stall without reaching critical AOA

Yes!  If you slow down too much, your plane will not be making enough lift to support its weight.  The plane will "sink" from its line of flight, which increases the AOA on the wing.
Then you stall.
This is especially true if your Center of Gravity is too far back, or (for builders), if the tail is too small.

There are also high speed stalls...I'm confused

No need to be.  A stall occurs when wing AOA exceeds its limit.  People stall at higher speeds because they are trying too hard to turn, for example, to reach a runway.
So the best ways to avoid stalling are to watch our airspeed (so we don't need a high AOA) and to not be too aggressive with the elevator.

You cannot stall without reaching the critical angle of attack. Stall is defined by airflow separating from the airfoil which happens at a certain angle which can be thought of identical in the flight envelope. It should be changed to: "No you can't. But if you slow down too much AND TRY TO MAINTAIN ALTITUDE you will have to increase angle of attack. When the angle of attack reaches your critical angle that is what we call stall speed.

@Jan no kidding.  The issue, especially with larger aircraft, is the sink leads to the stall. Your second to last comment sentence is exactly the point.

Yes, but it stalls because sink causes increase of the local AoA if you don't change the attitude (due to the extra vertical airspeed component). Your AoA sensor will show the increase, and if equipped with a stall warning, it will trigger.


text:
What is the formula used to display energy markers on HUD?
I would like to know what is the formula used to display energy markers on the head-up display (HUD) of fighter aircraft. Does it consist of Mach number or TAS or CAS?

Can you please provide an example?  Any photos?

Perhaps you are asking for the potential flight path angle (PFPA depicted by chevrons), derived from the total energy (sum of potential and kinetic energy)  or the velocity vector FPM/FPV depicted by a circle. Both are presented here. A view of the symbols on a PFD. They are used together: If the chevrons are above the velocity vector, the aircraft is accelerating.


text:
Why do the F/A-18 and the F-22 Raptor have horizontal stabilizer as well as canted rudders for pitch control?
F/A-18, F-22 Raptor have a horizontal tailplane as well as canted rudders? Why can't the horizontal tailplane done away with (as in the F-117) and have only the ruddervators for pitch control?

Since the F-117 basically is a flying wing, it doesn't have a horizontal tailplane by design. The pitch is controlled by the ailerons at the wing tips. No way the rudder on the F-117 can provide a large enough pitch.

The rudders on modern fighters are canted mostly to reduce their radar cross section. A straight vertical tail would produce a corner reflector in combination with the fuselage or the wing and would send radar waves straight back to their source. To reduce the detection radius, such a behavior must be avoided. The first aircraft to use this trick was the SR-71.
On the F-18 an additional reason was to move the tips of the vertical tails into the lateral position of the chine vortex: The wing's big leading edge extension produces a strong vortex at high angle of attack which improves the effectiveness of the tails and gives better yaw control. However, the bursting of the vortex would cause heavy buffeting, and an additional fix was needed to improve the fatigue life of the tails.
The horizontal tail is a necessity for pitch control and to trim the flap moments in the landing configuration. Just look at Boeing's entry to the JSF competition: The X-32 was initially planned as a delta with only vertical tails, but when the Navy refined their carrier operation requirements, Boeing had to add a conventional horizontal tail to achieve the required angle of attack and minimum speed.

Boeing X-32 (left, source) and the planned production version (right, source) with the added horizontal tail. The F-117 was an Air Force plane with very limited agility, so it could get away with a tailless design. Real fighters and carrier airplanes cannot.
Giving the horizontal tail dihedral reduces its effectiveness in two ways:

Angle of attack changes from pitch variations are reduced by the cosine of the dihedral angle, and
the vertical component of the aerodynamic force is also reduced by the cosine of the dihedral angle.

Note that the drag of a V-tail depends on the total lift created, regardless of its direction. Only the horizontal component is effective for pitch control, so a steeply angled V-tail is very ineffective for pitch control. In air combat the high drag will reduce performance when it is needed most.

They're very different aircraft, built to different requirements, meant to fill very different roles.
Large tails are good for pitch authority and high-alpha---which are good for maneuvering and dogfighting, but not very relevant to the F-117's missions.
The F-117 was a medium-altitude, tactical bomber that spent its life trucking around a pair of large, 2000 lb bombs. It wasn't expected to tango with opposing fighters, so maneuverability was less important, thus the small tail and very modest T/W ratio. Stealth kept it alive, not fancy footwork.
The Hornet classic (and Super Hornet thereafter) is a multirole fighter, expected to perform everything from fleet defense, SEAD, interdiction, recon, and of course CAS. It was made to handle extremely well at low-speed and high AOA. Pitch-rate and nose-pointing is very good---it will easily turn inside an F-16, albeit briefly (turn rate v. turn radius). Low-speed controllability is also crucial for landing on carriers. This is why it needs large tails
The Raptor is an air superiority fighter (with some multirole capability). Its job is going toe-to-toe with anyone else in the air. So all the classic performance parameters matter: T/W, acceleration, top speed, climb rate, turn rate and turn radius. It will out-turn a Hornet (instantaneous and sustained) and out-run an F-16 despite being twice as heavy as either. Large tails are even more important for control here, especially the very high altitudes at which the F-22 can fly.
In other words, the Raptor and Hornet need to be pretty nimble---the F-117 does not.

Here's a Super Hornet giving a little show. Watch it yank its nose around at 4:35 and 5:00.

The design philosophy of the F-117 was different from that of the F-22 (or F-18, which was not intended to be a stealth aircraft). The main design driver of the F-117 (in fact, practically the only one) was to reduce the RCS- the result being a distinctly non-aerodynamic design. The inclusion of separate horizontal stabilizers would've reduced the effectiveness of the design. The F-117 utilized the four elevons (a combination of ailerons and elevators) in lieu of the horizontal stabilizer, due to their location far back in the fuselage. No horizontal stabilizers were ever considered in the development of F-117.
The F-22, on the other had was a supersonic, high performance combat aircraft, which would require horizontal stabilizers for maneuverability (it is a super-maneuverable fighter which uses thrust vectoring). In absence of horizontal stabilizer, it would be very difficult for the F-22 or F-18 to reach their performance objectives, particularly for the carrier borne F-18.
In fact, there was a variant of F-117 which was designed to have a horizontal stabilizer- the unbuilt A/F-117X, which was expected to be a multi-mission aircraft (unlike F-117, which could barely do anything other than lob bombs). One main reason this design had a horizontal stabilizer was that the F-117 had quite high approach speeds, as the elevons didn't double up as flaps. The revised tail had horizontal stabilizers similar to F-22, which was used to reduce the descent rate and control the approach angle, which wouldn't have been possible with the original F-117.

On the F-18, the elevators do not generate enough downward force for takeoff. The rudders provide the additional force required. Visible in this video:

Notice that both rudders are inward on takeoff. Clearly if the elevators do not provide enough pitch control, the rudders along are not going to do it either.

The video is no longer available


text:
How does TACAN work?
How does the Tactical Air Navigation (TACAN) system work? How is it different from the VHF Omnidirectional Range (VOR) system? Please explain in the simplest possible way.

What is missing from the Wikipedia article about it?

How is TACAN different from the VHF Omnidirectional Range (VOR) system?

A very short question, but the answer calls for describing several techniques which are by themselves difficult to summarize without taking liberties with reality, so the post is rather long and should be read by sections of interest rather than totally at once. And for those not interested in the design techniques, fortunately there is a...
Short answer
Design principle:

A TACAN uses UHF to increase bearing precision. It consists on a single integrated system performing bearing and distance determination at once. In this system, the ground station is a transponder and the interrogator is on-board the aircraft (contrary to the SSR transponder). Frequency is like graduations on a scale, when frequency increases the graduations on the scale are more dense, and readings are more accurate.

A VOR works on VHF for bearing determination. No aircraft action is required to trigger the ground station signal which is permanent. To determine distance, another independent system, the DME, is used. The DME has been borrowed to military and is actually a TACAN without its bearing components (so it is a transponder interrogated by the aircraft).

When selecting a VOR frequency in a civilian aircraft, the avionics actually sets the VOR receiver on this frequency, and the standalone DME interrogator at some "paired" UHF frequency obtained from the ICAO standard pairing table (page 6). VOR and DME share nothing on board beyond the frequency pairing table.

Station antennas:

The original TACAN antenna is made of two small rotating drums with parasitic antenna elements (see details below). A TACAN can be installed on ships or mobile stations. The TACAN antenna is externally similar to a conventional VOR. A TACAN in Alaska during an exercise:

(Source: Wikipedia)

The cylinder contains the rotating antenna system. In more modern TACAN, the mechanical rotation has been replaced by electronically scanned arrays, reducing the size:

Transportable TACAN, source

Doppler VOR (DVOR) are more common than conventional VOR (CVOR), because they can be located on airfields (CVOR: See below for details). The DVOR antenna is a large circular array with a central reference antenna and a large counterpoise under the array.  VOR are sometimes colocated with a DME station, in that case there is a separate vertical DME antenna collocated with the VOR system.

Beijing (PEK) VOR/DME, DME antenna visible above the central VOR reference antenna. (source: Wikipedia)

Because the DME part is common to VOR/DME and TACAN, it is technically possible to associate a VOR to a TACAN to obtain a VORTAC station. Military use the TACAN, civilian use the VOR and the DME information of the TACAN:

A full TACAN in place of the previous DME antenna. Source

In addition VOR (CVOR/DVOR) uses Alford loop antennas which are horizontally polarized and radiate low on the horizon. They are sensitive to reflection on obstacles. An electrical counterpoise is required to hide the ground and raise the radiation angle. This artificial ground plane can be very large to be effective:

PFN Vortac (decommissioned), source

Signals:

A VOR transmits bearing information continuously.

A TACAN sends reply pulse pairs when interrogated (see the explanation below). These pairs convey both bearing and distance information.

A TACAN is usually more powerful than a VOR and has a larger range of use.

I'll focus on explaining bearing determination systems, and explain the DME as an integral component of the TACAN. In addition there are two types of VOR, conventional and Doppler, which work very differently even if they deliver compatible signals to the (unsuspecting) common receiver.

Bearing determination principle
The common principle of bearing determination is to send two signals from the ground station:

A reference signal telling any receiver around the current orientation of the active signal.

A variable signal allowing a particular receiver to determine when the active signal is "pointing" to the receiver (pointing is not the accurate word as the DVOR signals are omnidirectional, see more in this answer).

The receiver determines its relative bearing by comparing these two signals. Both signals are sine functions, the orientation value is represented by the current phase of this function. Both VOR and TACAN use this basic principle, albeit they realize it differently.
The signal phase has the major role in this story, so let's be sure we agree the meaning:

Any periodical (repetitive) signal can be seen as the result of a vector turning at some rate $\small \omega$. The sine function for angle $\small x$ is $\small y = sin(x)$. Applied to a sinusoidal wave of frequency $\small f$ and peak amplitude $\small A$, this becomes $\small y=A.sin(\omega t+\varphi)$ where $\small \omega = 2 \pi f$. The angle $\small \omega t+\varphi$, has been split between the phase $\small \omega t$ and the phase at origin $\small \varphi$. $\small \varphi$ is null if we start a cycle at time 0, this is usually the case. More simply, the quantity $\small \omega t$ represents how much the vector has turned at time $t$. It is an angle, reset after a full turn, therefore it indicates in the end which portion of a full cycle has already been spent (which phase we are in the cycle). Visually:

Phase angle of a sine wave
From that, it is clear that comparing phases of two signals with the same frequency (simple to do with electronics) is equivalent to comparing how much time one lags behind the other (time is actually difficult to measure).
VOR types
Conventional VOR (CVOR) and Doppler VOR (DVOR) stations are perceived identically by the receiver, though they transmit very different signals. The DVOR use tricks to mimic a CVOR and deceive the CVOR receiver. CVOR have nearly disappeared from sight because, due to their sensitivity to reflections, they cannot be located on airfields or close to roads. However en-route/high altitude CVOR can be found at isolated places, the reason is they are more compact and have a smaller cone of silence than DVOR and reflections can be minimized, e.g. when the VOR is located at the top of a hill.
Understanding the DVOR tricks without knowing how a CVOR works is difficult, and doesn't give clues on how the bearing is really determined. So I'm afraid we need to understand the CVOR before the DVOR.
Conventional VOR: CVOR
Early CVOR antenna used to be an array of four Alford loops at the corners of an imaginary square, known by their conventional names: NW, NE, SW and SE. NW+SE loops form the first pair, NE+SW loops form the second pair.

CVOR with four Alford loops
Alford loops are horizontally polarized and very sensitive to reflections on surrounding obstacles (multipath).
Recent generations of CVOR use a slotted antenna, which is a fixed cylinder with vertical slots (generally four slots):

CVOR with slotted antenna and the DME antenna on top. Source: AviaTecho.
A counterpoise is placed under the array to hide the VOR shelter and the ground and raise the radiation direction, it has the dual effect of minimizing undesirable reflection on the shelter and the ground and reducing the cone of silence above the VOR.
CVOR creates and uses reference and variable signals this way:

A low frequency generator creates three 30 Hz signals, identical except their phases. Two audio signals are derived from a reference signal: The sin signal has a phase at origin of -90° and the cos signal has a phase at origin of +90° (the point is sin and cos signals are in phase opposition).

The phase of the reference conceptually represents a direction and is often called the goniometer. As this signal frequency is 30 Hz, the imaginary direction it represents sweeps 360° 30 times per second (1,800 rpm, this is pure abstraction, there is no rotating parts in a CVOR).

A low frequency generator creates a 9960 Hz signal which is FM modulated by the reference. This signal is known as the reference subcarrier.

Conventional VOR block diagram

A HF generator creates a carrier of frequency f (f being the VOR frequency), this carrier is split in three parts:

one part is AM modulated by the reference subcarrier.
another is AM modulated by sin.
the last part is AM modulated by cos.

The HF signal with the reference subcarrier is sent to all antennas. This way the reference can be received identically regardless of the position of the receiver around the CVOR.

The two other HF signals have first their carrier removed, so that only the sidebands subsist. This is to prevent carriers to interfere in space, interferences must occur only between sidebands.

Then one signal is sent to the NW+SE pair of antennas, the other signal is sent to the other pair (remember the two pairs are perpendicular).

The space modulation magic does the rest. The sin and cos sidebands are added as field vector values, sometimes the individual amplitudes are added, sometimes they are subtracted, in variable proportion. This results in an unbalanced cardioid pattern (more precisely a Limaçon de Pascal) which rotates around the VOR antennas at 1,800 rpm, the direction being linked to the phase of the reference (or sin or cos, as they are all linked by fixed values).

The signal resulting from space modulation appears like being a carrier AM modulated according to the direction of the virtual "rotating antenna". The AM modulation is also a 30 Hz signal, and is known as the variable signal.

The resulting signal also contains the unmodified (and constant amplitude) carrier with its reference subcarrier.

CVOR spectrum

To determine the bearing (the radial) of the receiver relative to the CVOR, one only needs to compare the phase of the variable signal with the phase of the reference signal. Both are contained in the resulting signal. The phase of the reference signal and the phase of the variable signal are equal when the reference "points" to north (per principle at this time both phases have a value of 135°, the sum of 45° and 90°, but the actual value has no influence, only the phase difference is meaningful):

VOR: Determination of the bearing by comparing phases

Now we know the principle of the CVOR, it more easy to understand the principle of the DVOR. The DVOR was created to make up for some weaknesses in the CVOR: The CVOR is not terribly accurate unless the installation site is very carefully selected (no obstacle). That means isolated points, not airfields. That's not the preferred option for maintenance and this often precludes having the CVOR aligned with the runway for a VOR approach.

From CVOR to Doppler VOR, ensuring retro-compatibility
The lack of precision of the VOR is rooted in two design choices:

The antennas are close to each other, any default in their placement has great consequences in the accuracy.

The variable signal is AM modulated, AM modulation is deadly subject to errors created by electromagnetic noise and multipath.

In the Doppler VOR (once again... there are two types of DVOR, the single sideband and the double sideband, I'll describe the DSB here):

The two active antennas are at a large distance from each other (diametrically opposed).

The variable signal is FM modulated.

In order to be compatible with the CVOR receiver, other changes had to be made:

As the receiver still compares two signals, one being AM, the other FM, the reference signal must be AM modulated.

Because the result of the phase comparison is now inverted (variable minus reference becomes reference minus variable), the direction of rotation of the pattern must also be inverted (anti-clockwise instead of clockwise).

Because the pair of antennas used for the variable signal creates deliberately a Doppler effect, the reference must be sent on a specific central antenna preserved from the Doppler effect.

Doppler VOR: DVOR
The principle of a Doppler VOR is to create the frequency modulation by Doppler effect rather than by electronic modulation. The Doppler effect occurs with a moving wave source: In spite the source has a constant frequency, when it comes closer to the receiver the apparent frequency is higher than the actual frequency. How much higher depends only on the closure rate.

Doppler effect on train noise: Sound is higher-pitched at the front than at the rear
In the DVOR, pairs of opposed antennas (still Alford loops) are constantly switched on/off, scanning the full array anti-clockwise, the full scan being done 30 times per second. Actually there are two groups of antennas rather than two antennas involved to allow for blending (smooth transition from one pair to the next), but let's simplify for a second. From a receiver standpoint, the signal seems to come from a moving source, and therefore a Doppler shift will occur in a proportion which depends on the apparent direction of the move.

DVOR Doppler effect
To allow for compatibility with the CVOR receiver, this shift must be at most 480 Hz, 480 Hz being the FM swing of the subcarrier in the CVOR. A simple calculation shows the array diameter must be about 14 m (46 feet).
To generate the FM modulated signal, the unmodulated 9960 Hz subcarrier is sent on the "rotating" pair of antennas. The Doppler shift is maximum when the receiver direction is tangential to the pair trajectory and minimal when the pair is perpendicular to the direction of the receiver. This shift is exactly representative of the aircraft bearing and is the variable signal modulation we need.
From a radio signal perspective, only the sideband frequencies are used to transmit the 9960 Hz subcarrier (VOR frequency f +/- 9960 Hz). The carrier is itself sent on the central antenna, AM modulated by the reference signal. This way the carrier is not subject to the Doppler shift.
Bottom line... Like in the CVOR, the receiver sees the composite signal: A carrier AM modulated with a 30 Hz (which is the reference instead of the variable signal), with a subcarrier FM "modulated" as the result of the Doppler effect, at 30 Hz (the frequency of the scan, it now represents the variable signal instead of the reference) and with a swing not far from the expected 480 Hz.
Blending: If a pair of antennas were used one at a time, the number of measurable bearings would be equal to the number of antennas in the array (about 50). To create a more continuous scan (and therefore a larger number of measurable bearings), the antennas which precede and follow the main antenna are also fed by the subcarrier signal, but with a smaller power. This "blends" the transition from a scan position to the next one.
See also What causes the phase to change in a VOR? for a better explanation of the DVOR.
TACAN bearing
A TACAN is based on a stationary antenna plus a rotating parasitic system. The base antenna is vertical and is used to transmit a reference for the bearing measurement.
Parasitic elements in the aerial field refer to passive antenna elements added to the actual active radiator. A reflector decreases the gain on its side, a director increases the gain on its side (more). The well-known Yagi directional antenna (here in an horizontal polarization) has the two types of parasitic elements:

(Source, modified)
These elements are used in the TACAN, but they are rotating around the active element:

(Source, modified)

The central element transmits a constant amplitude signal used as a bearing reference.

A rotating drum with a reflector electrically adjusts the radiation pattern, adding a signal dip (low gain) that rotates at 900 RPM, which is equivalent to a 15 Hz amplitude modulation. The radiation pattern in the horizontal plan takes the shape of a cardioid:

(Source: Advances in Electronics and Electron Physics, Volume 68, modified)

Another drum with a set of 9 directors, mechanically linked to the first one, creates a 135 Hz (9x15) additional amplitude ripple over the 15 Hz modulation:

(Source: Advances in Electronics and Electron Physics, Volume 68, modified)

The TACAN signal isn't continuous, but only keyed (switched on/off) by bursts of information. Burst are of two kinds:

Reference bursts
DME responses.

Reference bursts are generated according to the orientation of the modulation pattern:

When the 15 Hz peak faces East a main reference burst namely North is sent. The burst consists of 24 pulses (12 Pulse Pairs)

with an asymmetric duty cycle.

An auxiliary reference burst is sent every 40°. The burst consists of 12 pulses(6 Pulse Pairs) with a symmetric duty cycle totaling 1440 pulses (720 Pulse Pairs)

DME pulses are send only in reply to an interrogation from an aircraft:

The aircraft sends a train of pulse pairs, which timing contains a random part (jitter). The transponder retransmits the same pulse train, with the same timing, but after a fixed delay (typcally 50 μs).

The aircraft correlates all pulses received with its own interrogation train. When the replies to its own interrogations are identified, it's possible to determine the delay and, subtracting the constant delay added by the transponder, the round-trip time, hence the distance.

If there is few aircraft DME interrogations, most of the time the TACAN signal is not keyed, therefore not transmitted. This lack of transmission would create a difficulty for the aircraft receiver:

To adjust its receiver gain (AGC) to counter fading.
To identify the 15 Hz and 135 Hz modulations.

The TACAN signal is therefore keyed at an approximate rate of 2,700 pairs of pulses per second, adding squitter pulses if necessary to fill the blanks (more in MIL-STD-291).
The DME pulse train is sent using the rotating radiation pattern. The receiver sees this train as being amplitude modulated, due to the strength variation of the received signal.

The 135 Hz signal has been removed for simplification (Source)
The 135 Hz modulation is used for the bearing determination. By comparing the time between an auxiliary reference burst and the subsequent reception of one of the 9 signal peaks, it is possible to determine the aircraft bearing relative to the ground station. The main burst (15 Hz) is used to disambiguate which of the 9 lobes was used, and therefore which of the 40° (360/9) sector is actually relevant for the bearing.

(Source: Advances in Electronics and Electron Physics, Volume 68. Modified)
In theory the use of the top end of the UHF band and the 135 Hz ripple increase the bearing accuracy by one order of magnitude compared to the VOR. In practical this is less, but still better than the VOR.

Nice answer. +1 Been wondering about this myself. Do you know if most military aircraft are equipped to read VOR also?

@TomMcW: Thanks! TACAN have larger transmission powers for a greater range, I don't know if it's really needed to receive VOR, but if it is, then it's a matter of adding an antenna, a receiver and an CDI, no big deal. It could be useful for fly non-precision civil approaches.

Thank you for the footnote - I was going to ask about that... :) I agree with @TomMcW - excellent answer!

C-130's have both VOR and TACAN receivers, and I'd suspect that most transport aircraft do as well, since foreign fields may be served by VOR/DME's rather than VORTAC's.

Great answer! With greater range & smaller size, the TACAN seems like the better technology, but outside of the military, the VOR seems predominant. What advantages does the VOR system have?

Thanks @RalphJ : I believe the VOR was designed with stationary antennas in mind for simple maintenance. Today it is easy to synthesize / beam form the 9th harmonic ripple of the TACAN using high resolution phased arrays and DSP chips, but at the time, they weren't available.

Typically (for you) fantastic answer. Semi-interestingly the picture you credit as Lambourne VOR (id: LAM which is in SE England) is actually credited on wikipedia as PEK in China

I@Jamiec: I don't know why I indicated LAM, with a checkerboard, it seems to be PEK. Thanks.

Well, the short answer is that it operates in the same way as VOR except it uses UHF instead of VHF - and is therefore less subject to distortion - and always incorporates DME so a range and bearing are both given.  VOR/DME is the civilian equivalent.

VOR/DME would be the civilian equivalent. VORTAC is combined civilian and military.

@TomMcW Cough, cough, er yeh.


text:
Means of protection against hunter-killer UAVs
I would like to know all existing technological means of defending an area against the MQ-9 Reaper or other hunter-killer unmanned aerial vehicles (UAVs) used by the United States in countries like Afghanistan, Syria, etc. Such means should either force the UAVs to leave the area or crash.

I hesitated to post my question here, on electronics.stackexchange.com, or on physics.stackexchange.com but I finally decided to post here because I think this community is the more appropriate but if my question is not adapted to be here, please move this question to the more appropriate StackExchange community.

Why the downvote ?

I have not voted, but asking for a list of everything ranked by price is not the best type of question on StackExchange. Perhaps if you asked more generally what options exist, or what potential weaknesses are, it would be a better question.

put on hold Where should I post this topic then?

Where is the freedom of speech here

@frenchstudent this is primarily a community of pilots, mechanics, and people interested in airplane design or aerodynamics. This question simply isn't a great fit for those types of people, and that's why it was closed as off-topic. Furthermore, it's hard to imagine there would every be a decisively correct answer, which makes it difficult for me to imagine it being a good fit for any Stack Exchange site. You're probably better off soliciting opinions in a forum somewhere.

By far the cheapest method for protecting a limited area would be to use an aerostat to carry aloft a jammer. Vehicles like the Reaper rely on a satellite uplink to maintain their command and control. As long as the aerostat is well above the altitude of the Reaper it can easily jam it. The cost of this option might be around \$1 million with an annual operating cost of \$200,000 and an effective diameter of about 10-20 miles.
A more expensive, but more flexible response would be to just shoot it down. To do this you would need an air surveillance radar, a high performance turboprop with machine guns like a Texan or Super Tucano, a pilot and a crew to operate the radar. With this method you could deny a pretty large area, maybe 100 miles in diameter easily, possibly more. The cost of this would be about \$3 to \$5 million plus annual operating costs of about $500,000. If you want to spend a bit a more a Yak-130 would be an excellent light attack jet to consider for anti-drone work. You might be able to find a used Yak for under \$10 million and it is a bitchin aircraft that can go double the speed of a Predator plus it has its own radar.
Missile systems would not really work because the types you would need to reach the altitude a Reaper operates at, are very expensive and complex (which is exactly why the Reaper flies at those altitudes). However if you could catch the Reaper while it was taking off or landing, a small missile like an RBS 70 would be even cheaper, assuming you could obtain that weapon.

I wonder if using a jammer (permanently) is an option. Wouldn't it prevent a lot of civil satellite applications, starting with GPS ones?

@mins The jammer only will affect a local area and will be on particular frequencies. A predator operates on the Ku-band so you will only jam that band which will not affect GPS which operates on L-band.

A drone is practically a type of aircraft and can be shot down using the same means as shooting down aircraft, and then some, like

missiles (surface to air or air to air).
If they are flying low, using guns in point or area defense weapons,
There are some other defensive measures under development like laser and microwave.
In case of UAVs being controlled remotely (as most of them are), the signals can be jammed.

This is a Glock 19.  Cost: $350

This is a 9mm bullet.  The Glock holds 15 of them. Cost: $12.99 for a box of 50

This is the ground control station for a Predator drone.

And this is what it looks like on the inside.

The Cheapest Way To Bring Down A Hunter-Killer UAV

Go to the ground control station.
Shoot everything.
Take control of the UAV.
Crash the UAV.

Total cost: $362.99

Being gunned down by military personnel trying... priceless


text:
In what manner was the Vympel R-73 (AA-11 Archer) a game-changer in comparison with NATO's missiles?
I have heard that when the Vympel R-73 air-to-air missile was introduced it was a game-changer.
I have also heard that after the collapse of the Soviet block it was tested by NATO (via re-united Germany) and NATO was quite impressed by it. According to one source, in close combat the MiG-29 was better than the F-16 by 2:1 and better than the F/A-18 by 1.5:1.
What was so special about it? How did they make it? Did they have better experiences? Or ideas?

The Russians brought some new ideas to the missile warfare when they mated the Vympel R-73 with Mig-29. The most important of these was the high offset sensor lock mode, which allowed the pilot to 'lock on' to the targer regardless of where the nose was pointed at. According to Peter “Stoini” Steiniger a JG 73 Pilot, who flew Mig-29s in East Germany,

The nice airframe in combination with one weapon was the killer: The Archer in [sensor lock] mode.” Introduced in the mid-1980s, the Archer AA-11 is a very capable heat-seeker with a greater range than the U.S. Sidewinder. “A simple monocular lens in front of my right eye enabled me to slew the seeker head of the missile onto my adversary at high angle off [target].” The Fulcrum’s ability to lock a missile even though its nose was pointed far away from its target “watered many eyes,” ...

The image below shows the missile aiming sight mounted on the helmet of a JG 73 pilot.

Image from airspacemag.com
This off boresignt advantage was not achieved by the western forces till they introduced the AIM-9X missile and the Joint Helmet-mounted Cueing System in 2002.
Aircraft-wise, the Mig-29 was a revelation to the west as the previous Russian designs have not been so sophisticated, so as to speak. The West was concerned enough with Mig-29 to start looking for new fighter ideas. Another important equipment in Mig-29 was the Infra Red Search and Track System (IRSTS), an idea for which the US is just warming up. Most of the exchange pilots, who flew the Mig-29 against the US F-15s and 16s were quite surprised and initial engagements usually went the 29s way, though techniques were later devloped exploting the Mig-29s' weaknesses. From an USAF exchange pilot:

From BVR (beyond visual range), the MiG-29 is totally outclassed by western fighters. Lack of situation awareness and the short range of the AA-10A missile compared to the AMRAAM means the NATO fighter is going to have to be having a really bad day for the Fulcrum pilot to be successful.
In the WVR (within visual range) arena, a skilled MiG-29 pilot can give an [F-15] Eagle or [F-16] Viper driver all he/she wants.

"Eagle" is presumably an F-15... do you know what "Viper" refers to, though? I'm not familiar with the nickname

@JonStory Viper refers to F-16. Its official name is 'Fighting Falcon', but is commonly called 'Viper' by pilots.

Hmmm, no idea how I missed that one, then, apart from the fact I'm not a pilot :p thanks

I don't know much about fighters but I'm scratching my head thinking, "before this you had to point the plane at something in order to shoot a missile at it?"

@TomMcW More or less... before high off-boresight missile were available, a pilot had to maneuver the aircraft so the FCR (Fire Control Radar) or the missile's seeker could obtain a lock on the enemy aircraft (aka the 'bandit'). Things get a bit more complicated if we start talking about radar-guided vs infrared-guided missiles, all-aspect vs rear-aspect etc.

@TomMcW most missiles are locked by pointing the seeker head at the target, a seeker head with a relatively narrow field of view. So yes, that means in practice pointing the nose of the aircraft at the target. The MiG-29/AA-10 combo meant the pilot could launch the missile and it'd get targeting data from the aircraft as long as the pilot kept his head pointed at it, basically. This was revolutionary at the time (and still is pretty uncommon).

Yes, the Russians had the better ideas.
The key was the slaving of the radar system to the pilot's helmet, called sight-controlled missile targeting: The missile would lock to whatever the pilot was looking at. In combination with the wide off-boresight capabilities of the aircraft's radar and the missiles, it even allowed to get a lock on aircraft flying actually behind it. When US F-16s met ex-GDR MiGs in exercises in the early 1990s, they were shocked to find how much superior the Russian design was.
From the second link:

With the Phazotron NIIR N019 Doppler radar (NATO designation "Slot
  Back") capable of detecting a target more than 60 miles away, infrared
  tracking sensors, and a laser rangefinder carried on the MiG-29, a
  pilot could track and shoot at aircraft flying below him. Also, the
  pilot's Shchel-3UM-1 helmet-mounted aiming device turned the MiG-29
  into a very dangerous threat once opponents came within visual range.
  No longer did a pilot have to turn his aircraft toward a target and
  wait for his missiles' sensors to "lock-on" before firing. Now, the
  pilot simply turned his head toward a target, and the helmet aimed the
  missile's sensors toward the target. This "off boresight" procedure
  gave the MiG-29 pilot a great advantage at close range.

According to this article, the main reasons were its exceptional mobility and accuracy. It can maneuver well enough to hit an aircraft in a 12 G turn, and has incredible accuracy, due to a direct connection with the pilots HUD, sophisticated infrared targeting, and a system called a "transverse control engine" (the details of which are apparently classified) to ensure that the target can't out maneuver it at the last second.


text:
Why do all new European fighter jets have delta wings?
Why do all new European fighter jets - Typhoon, Gripen, Rafale have delta wings? As I know, they were all designed separately. And they are not new either.
Is there any particular advantage that caused the Europeans to choose to do it like it is? Is it because of traditions? Or do they use the same software? (cheeky grin)

The accepted answer to this question tells you why but by answering the reverse - why aren't deltas used?

Well, it is a nice answer, but I still don't know, why all European manufacturers choosed delta wings.

...wait, you mean there are fighters that don't have delta wings?

No, they were not designed separately. They were designed by people who had all participated in collaborations before. The origin was the research into unstable configurations performed by MBB in Germany in the late 1970s by a modified F-104, the control configured vehicle F-104 CCV.

F-104 CCV (picture source)
As a result, MBB designed the Taktisches Kampfflugzeug 90 (or TKF-90), the first design of an unstable delta canard which promised unmatched maneuverability. Since Germany could not afford to develop the aircraft all by itself, collaborations were started with both Dassault and BAe, so that French and British engineers could learn of the advantages of this layout.

MBB TKF-90 concept (picture source)
First, BAe collaborated with MBB and joined the TKF-90 design, resulting in the European Collaborative Fighter proposal, only to continue on their own with two delta canard designs of their own, P.106 and P.110. P.106 had one engine and one vertical tail while P.110 had two of both, like the TKF-90. P.106 was rejected by the RAF, but went into a collaboration with Saab and eventually became the JAS-39.
To be fair, the first company to build and fly a closely-coupled delta canard was Saab with their Saab 37 Viggen. Saab has a long history of innovative work, beginning with ejection seats in 1942 and sweptback jets in 1948.

Saab 37 Viggen (picture source). In contrast to the TKF-90 it was an aerodynamically stable layout.
Meanwhile, MBB collaborated with Dassault in the Future European Fighter Aircraft (FEFA) program, so the French side learned of the advantages of a delta canard. Eventually, the French wanted less air-to-air capabilities and a smaller aircraft for better export chances, and the remaining FEFA partners continued in the European Fighter Aircraft (EFA) program which resulted in the EF-2000, while Dassault went it alone with the Rafale.
The EF-2000 is hampered to this day by this heritage. Its wing area was decreed by Maggie Thatcher and Helmut Kohl to be no more than 50 m² when a 60 m² wing would had resulted in a much more capable design. Next, the British engineers insisted on a straight leading edge, ignorant of the fact that only a cranked delta would provide good post-stall pitch characteristics. They also refused to accept a faceted design, and the German side could only rescue the "smiling intake" in order to reduce the radar cross section of the EF-2000 somewhat.

"Smiling intake" of the EF-2000 (picture source). The curved contour avoids corner reflections of electromagnetic waves.
And don't get me started on the odd location of the airbrake: On the center fuselage where it is least effective at high angle of attack and will blanket the single vertical tail. Designed by a committee with too many British engineers.

The smiling intake also accepts small carry-on luggage, it seems.

I didn't expected such a thorough answer! I alway though that the Typhoon is a pure English design. I don't understand the 60 to 50 square meters. And were the MBB or some of its staff a continuation from the second world war period? The period you mention was 30 years after the war, I am just curious why germans where the sort of a leader in that time.

@user3624251: BAe is practically the only company marketing the EF-2000, I guess that is why you got the impression they made it. A bigger aircraft has more range and can carry a bigger radar (just two things that depend on size; there are more), and the 50 m² meant fewer and smaller systems could be added. The comments are insufficient to explain the cultural differences between European nations.

OK, my next question will be about differences between the "english" and "german" school of aircraft design :-). But the part on Thatcher and Kohl - it was only an oversimplification to say that politicians decided or they really ordered such particular things as square meters of a wing?

@user3624251: Yes, they did. Watch this. Pay especially attention to the narrative of Roland Beamont at 19:42 into the report. Makes you shake your head at the arrogance and hubris of British government bureaucrats.

@Peter Kämpf Has the MBB built some prototypes of the TKF-90? Or a mock-up?

@user3624251: No prototypes that I know of. Only wind tunnel models and desktop airplanes. And one mockup which was on display at the 1980 Hannover air show.

Ouch. There is some palpable resentment here. Politics and engineering does not seem to be a good match.

Delta vs conventional wing has a good answer on some of the benefits/drawbacks of the design.
European military aircraft designers tend to prefer delta designs, dating back to the original Mirage, and even the Avro Vulcan bomber, whose design was actually begun in WW2.
The other two major makers of military aircraft, the US and the USSR/Russia, don't tend to use delta wings. Rare exceptions were the hybrid delta with tail design of the MIG 21, the North American XB-70, and most recently, the Boeing X-32JSF entry, which was changed to a tail design late in the competition due to Navy requirements. The last operational delta fighter in the US inventory was the F106 interceptor.
Why do European military aircraft designers prefer the delta wing?
The nature of the potential conflict plays a role in military aircraft design. European military aircraft, certainly in the past, were designed for fast sprints over relatively short distances where the delta's supersonic characteristics are a benefit, as in a NATO/Warsaw Pact conflict in Germany.
Russian and American aircraft are designed with longer distance conflicts in mind, where a good deal of the flying is at high subsonic speed, and the lower drag of the conventional wing reducess the need for refueling while in transit.

There are several other rare exceptions: F16, F18, F102 and F106 (which even have the world "Delta" in their names), F4, F14 in wing swept configuration, F15 etc. Delta wings in US designs is very-very common mainly because one of the great granddaddy of delta wings, Alexander Lippisch, worked for the US after WW2 (the other great grandfather of delta wings is of course Kalinin)

authors: Немања Стојадиновић